The invention relates to a method for producing a sandwich component, in particular an inner trim component for a motor vehicle. Furthermore, the invention relates to a sandwich component, in particular an inner trim component for a motor vehicle.
Such sandwich components made from multilayer composite material have been used for a long time, above all in the technology sector for air and space travel and above all distinguish themselves by their particularly low weight and their direction-dependent stiffness. Therefore, for example, a sandwich component can withstand particularly large loads (for example tensile stress) in a direction in parallel to the individual layers of the composite material, whereas different loading limits apply for loading perpendicular to the layers of the plastic component. In other words, therefore, by targeted use of different materials (for example honeycomb core, laminated fiber layer), a direction-dependent component stiffness is set and therefore, in particular, weight is saved.
For producing such a sandwich component, a method is known from DE 43 23 590 A1, in which a core layer made from a thermoplastic foam and thermoplastic cover layers are stacked and assembled in a single hot pressing procedure and formed into the component. The cover layers can here in particular consist of thermoplastic glass fiber woven material.
In the automotive field, trim parts which have been pressed or injected multiple times are used which have, however, a relatively high surface weight. Trim parts made from pressed parts, for example for door inner trims, consist, for example, of polypropylene natural fiber non-woven materials and have relatively low stiffness. Furthermore, there are also sandwich components, for example made from polyurethane materials, which, however, are relatively expensive and have high cycle times for their production.
A method is known from DE 10 2012 006 609 A1 in which a decorative layer is provided on at least one side of a heated sandwich semi-finished product, as well as a foam layer between the decorative layer and the sandwich semi-finished product. The heated sandwich semi-finished product is transferred into a potentially pre-heated forming press and inserted into a mold cavity in such a way that the side of the sandwich semi-finished product forms the visible side of the sandwich component with the foam layer and the decorative layer. In other words, therefore, to produce this sandwich component, firstly the sandwich semi-finished product (here consisting of cover layers and a paper honeycomb core, as well as PP films (polypropylene films) as an intermediate layer for cover layer connection) is heated in a heating press until respective thermoplastic fibers of the cover layers are melted. In connection to this, the foam layer and the decorative layer are arranged on the sandwich semi-finished product, wherein a mutual shaping of the decorative layer, the foam layer and the sandwich semi-finished product occurs in a forming press. The production of the connection between the material layers takes place here during the cooling of the sandwich materials. This method enables the cost-effective production of a so-called laminated sandwich component, in which any surface errors of the sandwich component are prevented particularly effectively, but operation requires increased production expenditure.
An object of the present invention is to provide a method in which a sandwich component can be produced with particularly low expenditure. Furthermore, an object of the present invention is to provide a sandwich component which is able to be produced particularly simply.
The method according to the invention is based on a core layer made from a foamed plastic and a cover layer which comprises reinforcing fibers and plastic fibers. Here, the plastic of the core layer has a (first) melting temperature which is higher than the (second) melting temperature of the plastic fibers of the cover layer. By the core layer being arranged on the cover layer, a multilayer composite is created. Using further process steps, this multilayer composite can be further processed into a semi-finished product. The multilayer composite or the semi-finished product produced therefrom is then heated in a heating device to a temperature which is lower than the first melting temperature (of the foamed core layer), but higher than the second melting temperature (of the plastic fibers of the cover layer). Then the multilayer composite heated in this way or the semi-finished product heated in this way is formed in a forming tool in order to generate the sandwich component.
Using the method according to the invention and the associated material system, it is ensured that the core layer and the cover layer do not form a substantial chemical bond during the heating of the multilayer composite, but that, instead of this, an adhesive, positive or mechanical connection is produced between the core layer and the cover layer. Due to the fact that, during the heating of the multilayer composite, a temperature above the melting temperature of the cover layer, but below the melting temperature of the core layer is selected, only the thermoplastic portion of the cover layer is melted. The foamed plastic of the core layer, however, does not melt and therefore remains almost stable during the processing. The hot cover layer(s) of the heated multilayer composite are consolidated during the forming in the forming tool, without the hot foam being substantially compressed. The form stability of the hot foam, the formability of the cover layer(s) and the counter pressure of the hot foam in the forming tool are thereby high enough to achieve consolidation of the cover layer(s).
Using the method according to the invention, it is therefore possible that the foamed plastic of the core layer remains approximately stable during the production process of the semi-finished product and does not collapse in on itself. Furthermore, the thus produced semi-finished product has particularly good forming properties.
Advantageously, a core layer which has open pores at least on its surface is used as a core layer. In other words, the provided core layer has an open-pore foam or at least the surface of the provided core layer has open pores or a rough, unclosed surface. The latter can occur, for example, during the production of corresponding foam plates which serve as an initial material for the core layer, by sawing out the foam plates from large foamed blocks. Alternatively, the surface of a closed-pore core layer can be pre-treated by needling or wetting or another means of roughening.
The cover layer advantageously comprises a thermoplastic fiber-reinforced textile structure, so a hybrid textile, such as, for example, a non-woven material, a woven material or a scrim made from reinforcing fibers and thermoplastic fibers which later form the matrix of the cover layer. Corresponding reinforcing fibers can, for example, consist of glass, carbon, aramid, or natural fibers or similar.
The use of unconsolidated cover layers made from hybrid textiles consisting of a reinforcing fiber (e.g. glass, natural, or carbon fibers, etc.) and a thermoplastic fiber which forms the matrix after the heating/forming of the multilayer composite is particularly advantageous, because unconsolidated materials have better forming behavior than consolidated. In this case, the consolidation of the cover layer only occurs in the forming tool/pressing tool, where the hot cover layer is consolidated without the hot foam of the core layer being substantially compressed, and where an impregnation of the reinforcing fibers by the melted thermoplastic fibers (preferably PP fibers) occurs. Since the cover layer is therefore only consolidated in the forming tool/pressing tool, the properties, in particular the degree of consolidation, of the cover layer can be adjusted by the foam pressure. Here, for example, a low consolidation of the cover layer can lead to an increase in the stiffness of the sandwich component since the thickness and the moment of inertia of area are increased. Furthermore, due to a low consolidation of the cover layers, surface errors on the component which, for example, are set due to inhomogeneous non-woven material cover layers, can be prevented. The form stability and therefore the counter pressure of the hot foam is sufficient to consolidate the cover layers sufficiently. A further advantage of the use of unconsolidated semi-finished products consists in that they are substantially more cost-effective.
It is particularly advantageous to use a hybrid non-woven material/hybrid needle-punched non-woven material having PP fibers as a cover layer, since this has particularly good expansion properties, high material isotropy, low costs and global availability. Due to the high expandability, such an unconsolidated non-woven material cover layer is particularly well suited to forming and to the formation of a thin cover layer on the hot, pressure-sensitive foam core layer. If, however, a woven material is used for the cover layer, then this leads—due to the clearly lower expansion property—to an increased loading of the foam during the forming in areas with small radii, since here the foam is loaded heavily with pressure due to the low expansion property of the woven material.
In an advantageous development of the invention, the cover layer additionally comprises a melt layer made from a thermoplastic having a third melting temperature which is lower than the first melting temperature and, as a maximum, as high as the second melting temperature. This melt layer is preferably a thermoplastic film, but the melt layer can also be formed by a local, thermoplastic enrichment or thermoplastic coating of the cover layer. The melt layer advantageously consists of the same thermoplastic material as the thermoplastic portion of the cover layer. Using the melt layer, the cover layer connection to the core layer can be improved and the core layer itself can be protected from moisture. The melt layer is arranged between the core layer and the fibers of the cover layer during the formation of the multilayer composite. During the heating of the multilayer composite to a temperature above the melting temperature of the melt layer, but below the melting temperature of the core layer, the melt layer (and potentially a thermoplastic portion of the cover layer) is melted. The melted thermoplastic material of the melt layer here penetrates open pores of the foamed plastic of the core layer and therefore forms a mechanical and anchoring and/or abrasive bond to the core layer. The melted thermoplastic of the melt layer is bonded to the cover layer either by mechanical anchoring in the relevant fiber non-woven material of the cover layer or to the likewise melted thermoplastic portion of the cover layer.
In a particularly advantageous embodiment of the invention, it is provided that the fibers of the cover layer are produced from polypropylene (PP) and the core layer from polyethylene terephthalate (PET). Furthermore, the optionally provided melt layer can also consist of polypropylene (PP). Polypropylene has a melting temperature of approx. 160° C., whereas polyethylene terephthalate only melts from approx. 250° C. It can thereby be ensured that the respective melting temperatures of the melt layer and the fibers of the cover layer as well as the core layer are far enough away from each other that a reliable implementation of the method can be ensured during heating of the multilayer composite. Furthermore, polypropylene and polyethylene terephthalate are relatively favorable initial materials which can additionally be bonded cost-effectively to a material composite without forming a chemical bond with each other.
According to a further advantageous embodiment of the invention, it is provided that an additional layer having a fourth melting temperature which is higher than the second melting temperature is arranged on the cover layer, forming the multilayer composite. The additional layer can, for example, be produced from PES or polyamide (PA). Due to the fact that the additional layer has a melting temperature which is higher than the second melting temperature, an adhesion of the multilayer composite to the heating device can be prevented in which the multilayer composite is heated during the production of the sandwich component.
A further advantageous embodiment of the invention provides that a decorative layer, in particular together with a further melt layer made from the same thermoplastics as the other melt layer, is arranged on the cover layer, forming the multilayer composite.
A further advantageous embodiment of the invention provides that the layers of the multilayer composite are connected to a semi-finished product at least in regions before the process steps of heating/forming.
The handling of the thus produced semi-finished product therefore hardly differs from a single-layer material, for example from a non-woven material, and additionally has a very high flexibility. Manufacturers of pressed, injected or back-injected components in which such a semi-finished product is used therefore no longer have to have partly very costly sorting devices in order to be able to produce corresponding sandwich components from the semi-finished product produced according to the invention. The semi-finished product production, in particular the arrangement of the individual layers of a sandwich component, can therefore be decoupled from the actual production of the sandwich component (by heating and forming). In this way, it is possible to decouple the production of the semi-finished product for a fiber composite component from the actual production process of the sandwich component in time and/or in space. Due to the partial connection of the individual layers to a preconfigured multilayer composite, the semi-finished product produced with the aid of the method according to the invention is able to be stored and transported; the semi-finished product can therefore, for example, be produced separately at a manufacturer of semi-finished products (e.g. a manufacturer of foam material or a manufacturer of non-woven material) and then can be transported to a component manufacturer who produces sandwich components from the semi-finished product. In this way, a clear simplification of the production process of the sandwich component following the production of the semi-finished product can be achieved. In particular, the component quality can thereby be increased and the cycle time during the component production can be reduced. Furthermore, the production and storage of the semi-finished product can be outsourced to a manufacturer of semi-finished products, whereby system investments can be reduced for the component manufacturer.
Alternatively, the semi-finished product can be supplied directly, so without intermediate storage, to the processing process, by means of which the sandwich component is produced. In this case, the production of the semi-finished product is coupled directly to the production of the sandwich component, without the semi-finished product being stored intermittently.
The semi-finished product can be produced in the form of a continuous material and arranged in roll form or can be configured into semi-finished product component parts.
After the connection of the layers to generate the semi-finished product, expediently in a further step, a rolling up of the semi-finished product into at least one semi-finished product roll and/or an assembly of the semi-finished product into several component parts as well as the formation of at least one component part stack of the component parts occurs. In a further method step, a provision of the semi-finished product to the finishing device occurs by unrolling the at least one semi-finished product roll and distributing the unrolled semi-finished product into several unrolled parts and/or unstacking of the component parts of the at least one component part stack. After this, the completed sandwich component is produced from at least one unrolled part and/or at least one component part in the finishing device by heating and forming.
The semi-finished product produced from the core layer as well as the at least one cover layer is therefore either rolled up into a semi-finished product roll and, additionally or alternatively, divided into the component parts, which are also referred to as plates, and stacked up into the component parts stack. The thus produced semi-finished product already comprises all desired layers of the plastic component, wherein additionally, for example, a decorative layer can also be provided which provides the component semi-finished product and therefore the plastic component formed therefrom with a particularly high quality. This decorative layer can even be added only after the heating of the semi-finished product for protection of the material. Depending on whether the semi-finished product is rolled up into the semi-finished product roll or is already divided and therefore configured into the several component parts having the desired length, the semi-finished product is still only unrolled in the finishing device and the unrolled semi-finished product is divided into the unrolled parts with lengths as desired or the component parts which already have a length as desired due to the assembly are unstacked from the component part stack. Correspondingly, no further layers have to be added to the semi-finished product in the finishing device, but the at least one unrolled part (of the semi-finished product roll) or the at least one component part (of the component part stack) merely undergoes the heating and forming described above in order to produce the sandwich component from the semi-finished product.
The sorting of the individual layers (here: core layer, cover layer and potentially additional and/or decorative layer) of the sandwich component is therefore not coupled to the further processing process. In other words, the production of the semi-finished product can therefore occur in the prefabrication device and the semi-finished product can correspondingly be transported as a semi-finished product roll or component part stack to the finishing device. The finishing device can correspondingly be formed particularly simply since no further tools must be provided for additional application of further layers to the semi-finished product. The individual sandwich layers can therefore be processed into the semi-finished product in the preliminary stage, so in the prefabrication device, wherein only the heating and forming of the semi-finished product occurs in the finishing device. It is therefore possible to decouple the production of the semi-finished product for a fiber composite component from the actual production process of the fiber composite component in time and/or in location.
Advantageously, for the production of the semi-finished product, the core layer and the cover layer (and potentially further layers) are connected using heat; this occurs in a prefabrication device which can be located with the manufacturer of the sandwich component, but alternatively also with a supplier.
In an advantageous embodiment of the semi-finished product production, the layers of the multilayer composite are connected by local melting of the cover layer, and the layers of the multilayer composite partially connected in this way are then preconfigured into the semi-finished product. Alternatively, the cover layer can be connected completely to the foam material core layer; in this case, instead of an only local heating and melting of the thermoplastic plastic of the decorative layer, this is completely melted and therefore also completely connected to the foam material core layer.
In particular, it is advantageous to connect the layers of the multilayer composite to each other continuously by means of a heated roller belt or a heated roller press. A particularly high production rate can thereby be achieved during the production of the semi-finished product. The semi-finished product is here produced in the form of a continuous material and can, for example, be rolled up into a roll.
Alternatively, the layers of the multilayer composite can be connected to one another discontinuously by means of a heated pressing tool. In other words, a pressing unit which is heated in a stationary manner is therefore used, wherein in this case, the semi-finished product is preconfigured directly and, for example, can be provided in the form of cuttings or similar. Alternatively, the layers of the heated multilayer composite can be connected to one another discontinuously by means of a cold pressing tool.
Several consolidating surfaces can be formed on the semi-finished product, at which the cross-section of the semi-finished product is locally compressed more strongly than regions which are different to the consolidating surfaces.
Alternatively to the thermal connection of the layers of the multilayer composite, for the production of the semi-finished product, the layers of the multilayer composite can also be connected to one another mechanically, in particular by needling. This is recommended in particular if the cover layer comprises a fibrous web and/or fibrous non-woven material; furthermore, the cover layer also advantageously comprises a melt layer made from a thermoplastic plastic. The fibrous web and core layer are then connected by piercing at least one needle having a barb into the core layer and the fibrous web and then guiding the needle out from the core layer and the fibrous web. Here, during piercing and/or pulling out of the needle, single or multiple fibers of the fiber web and/or fiber non-woven material are hooked with the barb and anchored mechanically to the core layer during piercing and/or guiding out of the needle. Alternatively or additionally, the needle can firstly pierce the fibrous web/fibrous non-woven material and only then the core layer, such that the needle already pushes fibers through the core layer during piercing, which causes a mechanical anchoring of the core layer to the fibrous web/fibrous non-woven material.
In a preceding method step, firstly a fiber mixture can be provided which comprises the thermoplastic fibers and the reinforcing fibers. Then, this usually inhomogeneous fiber mixture can be processed into the fibrous web by carding. Furthermore, an additional layer, so an upper layer, made from a material having a higher melting temperature than that of the thermoplastic fibers can be arranged on the fibrous web. This additional layer can in particular consist of a polyester, polyamide or of a glass material and causes adhesions to a surface of a heating device serving to heat the semi-finished product to be prevented.
After production of the sandwich component by heating and forming the multilayer composite or the semi-finished product, in a further process step, at least one plastic element can be fixed to the sandwich component produced in this way. The plastic element can in particular be a stiffening element. Such stiffening elements can, for example, be implemented by injected or adhered ribs, as well as by other material accumulations or beading or depressions on the plastic component. Therefore, the possibility exists of an additional and local stiffening of the sandwich component which particularly conforms to the requirements by means of such stiffening elements and connection elements to adjacent components.
Alternatively, after the forming of the semi-finished product, at least one element is injected onto this by means of the same tool, and in such a case, by means of a combined injection pressing tool. In other words, optionally, therefore one or more plastic components or elements serving as reinforcing elements can be injected onto the semi-finished product in the forming tool. The injection molding material can here contain filler or even reinforcing materials. In a simple way, a pressing procedure can thereby be combined with an injection procedure during the production of the sandwich component. During the production of the sandwich component, this can therefore remain in one and the same tool until its completion. Costly handling tasks during the production of the sandwich component therefore do not have to be carried out, such that the sandwich component can be produced quickly and with particularly low cost.
The sandwich component according to the invention, in particular inner trim component for a motor vehicle, is produced by means of the method according to the invention for producing the sandwich component or an advantageous embodiment of the method according to the invention for producing the sandwich component. In comparison to pressed components, the sandwich component according to the invention has a particularly low specific weight. Furthermore, this can be produced particularly cost-effectively and efficiently, since the semi-finished product is used to produce the sandwich component. Additionally, the sandwich component can comprise, to a certain extent, recycled materials, whereby a particularly good ecological footprint is able to be achieved.
Further advantages, features and details of the invention result from the subsequent description of preferred exemplary embodiments and by means of the drawings. The features and feature combinations referred to above in the description as well as the features and feature combinations referred to below in the description of the figures and/or shown solely in the figures are not only applicable in the respectively specified combination, but also in other combinations or alone, without leaving the scope of the invention.
Exemplary embodiments of the invention are explained below by means of schematic drawings.